The present invention relates to a field emitter to be used in various devices including a nanotube-based display and a microwave amplifying device, and, in particular, to a field emitter used in a display device, using a carbon nanotube as the emitter material. Herein, xe2x80x9cdisplay devicexe2x80x9d is intended to cover all of other display devices that use a field emitter.
Since it was first introduced in 1968, the field emission display (FED) has been continuously researched and developed as the next generation of display devices following the CRT (Cathode Ray Tube), TFT-LCD, and a large screen PDP.
In such field emission displays, a field emitter which incorporates the electron gun of a CRT with a material such as a metal (mainly, molybdenum), a semiconductor, or diamond has been considered. Since 1995 when the use of a carbon nanotube as the emitter material was suggested, much research and development associated with the use of the carbon nanotube have been performed.
Using the carbon nanotube as an emitter has many advantages. Because the carbon nanotube emitter is much thinner than a conventional emitter, high electric current can be created with the application of low voltage. Also, increased redundancy resulting from a large number of tips and the unique bonding characteristics of carbon guarantee a higher structural stability than that of a metal emitter.
Suggested carbon nanotube manufacturing approaches include:
First, carbon nanotubes are vertically grown on a substrate covered with a catalyst such as nickel by passing hydrocarbons across the substrate using a chemical vapor deposition (CVD) method;
Second, multiple carbon nanotubes formed using either an arc discharge or a laser ablation method of prior art are then mixed with a metal adhesive agent and arranged on the substrate; and
Third, a set of parallel carbon nanotubes formed by applying bias to aluminum is immersed into an acidic solution. The aluminum oxide film is allowed to erode continuously, forming (using a so called anodic alumina method) regularly perforated, fine holes thereon, through which hydrocarbons are passed.
FIG. 1 shows a schematic representation of a conventional, uncoated carbon nanotube. The arrow indicates the direction of electrons (xe2x88x92e) emitted when a voltage is applied, causing the carbon nanotube to act as a cathode. In practice, a large number of nanotube tips are employed, but herein, only one representative nanotube is shown.
Despite the efforts, problems with structural deformation or destruction have not yet been overcome, which results in instability or interruption of the carbon nanotube operation.
An emitter becomes nonfunctional for one primary reason. After an accelerated electron collides with a phosphor molecule, causing the desired emission of light, the positive ion dislodged from the phosphor collides with the emitter itself. For this reason, the level of uniformity, stability and durability of a display screen required for commercial use has been unattainable.
Accordingly, in view of the previously mentioned problems, the objective of the invention is to provide a carbon-based nanotube field emitter capable of greatly improving the performance of a field emission display. This objective is achieved by coating the tip of the carbon nanotube with a semiconductor or insulating layer with a high degree of hardness, several nanometer (nm) thick. The layer protects the tip from a collision with external particles while permitting electrons to emit freely, thereby establishing the necessary durability and stability of the carbon nanotube as well as reducing the required voltage applied thereto.
In accordance with one embodiment of the present invention, a field emitter comprises a semiconductor or insulating layer deposited thereon by evaporating the semiconductor or insulating layer on the carbon nanotube using an electron beam evaporation method.
In accordance with the other embodiment of the present invention, a field emission emitter comprises a semiconductor or insulating layer deposited on the carbon nanotube by sputtering argon on a semiconductor or insulator to knock out the constituent atoms and inject them onto the carbon nanotubes.
In addition, it is possible to deposit a semiconductor or insulating layer on a carbon nanotube by using all methods used for producing a very thin molecular layer such as a laser ablation method, a conventional CVD method and the like.